Froth control in ore flotation



Patented Sept. 11, 1934 UNITED STATES FRO'IH CONTROL IN ORE-FLOTATION Lyle M. Barker, Orel E. Young, and Oliver 0. Ralston, Clarkdale, Ariz., assignors to United Verde Copper Company, Clarkdale, Aria, a corporation of Delaware No Drawing. Application April 10,1929; Serial No. 354,168

3 Claims.

the percentage and purity of the ore recovered.

may be increased without materially increasing the cost of the recovery.

Another object of the invention is to provide a method of controlling the selectivity and frothing condition of collecting reagents so as to maintain the optimum collecting power with the most desirable working condition of the froth.

Another object of the invention is to provide a method of controlling the flocculating power of collecting reagents so as to permit the use of materials known to be powerful collecting reagents without producing a refractory or unworkable froth.

Another object of the invention is to provide a method of controlling the frothing condition in froth flotation by controlling the degree of flocculation of the floatable mineral particles.

Various other objects and advantages of the invention will appear as this description proceeds.

This invention is based on our discovery that mixtures of collecting reagents have important effects on the qualities of flotation froths in spite of the fact that frequently none of the collecting reagents used in such a mixture have any appreciable frothing powers in themselves, and that the character of the froth may be controlled independent of the frothing reagent by controlling the degree of flocculation of the mineral particles gathered together by the collecting reagent. Some of the most powerful and selective collectors, if used in amounts capable of collecting all the desired mineral, cause a type of froth which we describe as over-flocculated, for reasons set forth herein. We have discovered, however, that if these powerful collectors are used simultaneously with less powerful collectors, which are less highly flocculating, the undesirable condition of over-flocculation can be controlled, froth of exactly the desired physical characteristics can be produced and yet theadvantage of greater selectivity of the powerful collector retained. For instance, froths produced with such powerful collectors as the amyl xanthates, in proper amounts to produce good extractions, are over-flocculated and not commercially workable,

whereas by using less of the amyl xanthate and substituting an ethyl xanthate, a froth of excellent working qualities is produced while the collector is still of a high collecting power and high selectivity. I I

While flocculation has been regarded as of importance in froth flotation, no accurate definit-ion of the degree of flocculation can be made. The eflect of overor under-flocculation on the characteristics and workability of a froth are however easily recognized. In flocculation, a finely divided suspension of solids or liquids can be caused to coalesce into aggregates or fioccules containing two or more of the ultimate particles each. The degree of flocculation is dimcult to define for the reason that some of the particles involved are frequently too small to be resolved by the microscope, and therefore the average number of particles gathered together in each floccule or floc is unknown. The average diameter of the flocs might be taken as a measure, at least for the bigger flocs, but the usual reference to degree of flocculation is qualitative only; at one end of the scale being highly flocculated ore pulps and at the other end being highly dispersed or completely deflocculated pulps. A completely deflocculated suspension implies that the particles are completely wetted by water, and hence more diflicult to treat by flotation.

Flocculation is usually controlled by the electrolytes in the solution and also by other colloids dispersed in the solution, and, inasmuch as the desired mineral particles must be flocculated to at least a certain undefined degree, flotation must be carried on in water containing electrolytes, the electrolytes being added, if not already present.

When excessively large flocs of the desired flotative minerals are formed, the froth behaves in a very characteristic way which we would describe as over-flocculated. Instead of the usual well-known easily flowing, brittle froth of convenient volume familiar in commercial flotation, the addition of suflicient amounts of the agents which cause over-flocculation causes the froth to decrease in volume, become tough and somewhat of the consistence of mayonnaise, even shrinking to a thick heavy scum; Such froth is extremely difficult to remove from any flotation machine, big fioccules in the scant froth will lose their air bubbles, break away, sink and be rafted up once again by more bubbles only with great difliculty. The pulp level in the flotation machines must be raised so close to the overflow lip that if mechanical rakes are being used to force the refractory froth off the machine too much pulp is slopped out with it. Therefore, poor recovery of desired mineral is the usual result and the rough concentrate needs retreatment in another flotation machine. The addition of more frothing reagents, like pine oil, to an over-flocculated pulp, will frequently prove of no avail in producing a more voluminous, tender froth, and the usual remedy is to cut down the amount, or discard entirely the powerful flocculator.

In pulps where considerably lower flocculation of the desired minerals obtains, approaching the condition of complete deflocculation, the froth produced may become more voluminous and at best is poorly mineralized and watery. The condition can be called under-flocculation but is usually called over-frothing. In flotation machines of the usual type an inadequate amount of the desired mineral is carried off the machines in the time available, both on roughing and cleaning units, and again the result is poor extraction and sometimes poor grade of concentrate.

Briefly, over-flocculated froths are those in which the mineral burden per unit of bubble surface is excessive, due to the tendency of the min- I eral particles to draw closely together. The other extreme of under-flocculation or over-frothing is characterized by thin watery froths that are underburdened per unit of bubble area. Both of these extremes are undesirable for the reasons mentioned above.

Between the two extremes of over-flocculated and over-frothing conditions lie the optimum conditions desired for commercial froth flotation concentration. The usual method of attempting to secure these conditions is by empiricism, testing out numerous mixtures of difierent reagents in different amounts until a series of conditions are discovered which. happen to fit the ore in question. On account of this practice, it is quite commonly stated that each ore is a problem in itself, thus justifying this haphazard means of investigation.

Flotation reagents are classified roughly into three-classes, frothers,- collectors and modifiers and, in the usual practice, these are used in certain proportions, each to contribute a certain result. The function of each is hereby discussed.

The frothers are used to form a froth of workable consistency which will float on the pulp and support the mineral particles, collectors are reagents which act to selectively collect the mineral particles to be recovered and cause them to rise to the top of the pulp with the air or froth bubbles and modifiers are used to control either the frothing or the collecting power of the other reagents used or both.

Control of froth volume and consistence has in the past been attained mainly by (1) proportioning the frothing and collecting reagents relatively to each other; (2) changing the amounts of frothers independently; (3) choosing modifying agents and applying them in such amounts as to give the desired type of froth." We now present a new method of froth control not heretofore known and consistingin use of two or more collectors, one at least of which tends .to produce over-flocculation if used in sufllcient amounts and one at least which tends toward production of under-flocculation or over-frothing and by use of suitable proportions of these oppositely acting collecting reagents to obtain -,froth's of exactly" the desired mechanical characteristics and capable of producing superior metallurgical-results without necessitating modiflcation of the frother or the use of modifiers which, in themselves, are neither frothers nor collectors. By the use of our invention, promising collectors which show high selectively but cause non-commercial or poorly working froths, due to over-flocculation, may be corrected in their action, thus making it unnecessary to search for particular collectors which, in themselves, give both the desired mechanical consistence of the froth and highest metallurgical selectivity and recovery.

One application of our method may be illustrated as follows, but it will be understood that many other applications of the method disclosed herein may be made by persons skilled in the art either with collectors now well-known or collectors subsequently to be discovered: One of the common frothers used in connection with xanthate collectors is steam-distilled pine oil, and the xanthate, principally used, has been potassium or sodium ethyl xanthate, although the xanthates made with higher alcohols are known to possess similar or improved collecting qualities in comparison with the xanthates made with ethyl alcohol. xanthates made from butyl alcohols have been in limited use and xanthates made from several of the amyl alcohols have had a good reputation. The potassium amyl xanthate made from the amyl alcohol known as di-ethyl carbinol has had a limited commercial use and likewise the xanthates made from iso-amyl alcohol. Such amyl xanthates havev not met great success, however, due to their tendency to produce over-flocculation of the floatable minerals and hence unmanageable froths, as previously described. By our invention, however, we can retain many of the valuable effects of the higher erals like chalcopyrite or galena into froths in the presence of other sulphide minerals, their use is highly desirable and by'controlling the degree of flocculation and hence the character of the froth by simultaneously using a less powerful collector, we are able to retain the desired maximum selectivity and still have a highly workable froth.

The proportions in which the strongly flocculating collector and the more weakly flocculating collector are used vary with each case. instance. when treating United Verde schist, an ore containing 10% chalcopyrite, 18% pyrite, 23% quartz, 44% chloritic silicates and minor amounts of other minerals, in a pulp made barely alkaline tophenolp'hthalein' with lime and with each ton of ore using 0.10 lb. pine oil as a. frother, over-flocculation resulted when 0.10 lb.

potassium amyl xanthate was applied as a collector and no adjustment of pine oil xanthate ratio, or substitution of other frothers for the pine oil, gave satisfactory results, the extraction falling of! if the amount of amyl xanthate were was removed although at times the amount of amyl xanthate could be further out with advantage, in lieu of the use of an alkali ethyl xanthate it will be understood that other weak flocculators such as phospho cresylic acid may be used. The exact proportions of the strong and weak flocculating collector may be left to the discretion of the operators of the flotation machines, who can tell from the appearance of the froth, described elsewhere in this application, when it is performing properly. A froth condition approaching more nearly to over-flocculation than to overfrothing has been found by us to give the highest grades of concentrate with modern collectors.

With the ethyl xanthate alone as a collector the above described United Verde schist ore can be concentrated to give an average extraction of 92.5% of the copper and a concentrate which higher grade concentrate is more easily thick ened without a persistent froth piling up on the thickeners and is also more easily filtered, giving thicker, dryer filter cakes, all of which are important advantages.

Conditions vary with ores and the amount and type of alkalinity or acidity or other modifier present, so that a reagent which is a strong fiocculator under one set of conditions may be weak under others. With United Verde schist ore in a pulp made alkaline with trona or sodium carbonate, over-flocculation is observed with either phospho cresylic acid or sodium ethyl xanthate as a collector whereas these do not cause over-flocculation in a pulp made alkaline with lime. With Utah copper ore in a trona circuit, ethyl xanthates cause over-flocculation but in a lime circuit, they do not and in a lime circuit phospho cresylic acid will cause overflocculation. In any case, the use of a powerful collector which, however, causes over-flocculation to an undesirable degree, can be continued by reducing the amount ofthe powerful collector and supplementing the same with a less powerful collector which decreases the tendency toward over-flocculation.

In general, therefore, our invention contemplates the use of a powerful collector which tends to produce over-flocculation and the use of a less powerful collector to control the degree of flocculation and, hence, produce a commercially workable froth with a higher grade concentrate or ahigher extraction or both without material increase in cost.

For a practical field test, or as a more explicit if sufficiently flocculated to be distinguished by the naked eye the feathery to globular floccules can be observed in the resulting pulp. A better method of study is to pull aside the scanty froth in a quiet portion of the flotation machine, ex-

posing a surface of bare pulp and individual floccules will then be observed to come up to the bare surface, soon coalescing with each other to form a continuous rich looking scum in which individual floccules are no long distinguishable. As conditions are improved and over-flocculation diminished the volume of froth increases, the size of the floccules entering the bare area is smaller and finally they are too small to be distinguishable without the use of magnifying glasses, the frothing conditions having been improving during these changes in flocculation.

We are fully aware that in the earlier flotation practice, in which was used mixtures of indefinite and even chaotic chemical composition, like coal and wood tars and other distillates from coal, wood or crude petroleum, adjustment of reagents was haphazardly obtained but thefactors-favorable to production of satisfactory froths were not recognized. Most of these oily substances acted both as frothers and collectors-possibly even as modifiers, and the benefit of the individual unknown constituents was obscured. In fact, most of these nostrums were too insensitive or nonselective to permit recognition of such effects as we have described for the more modern collectors, most of which are definite chemical compounds of reasonable purity.

We are also fully aware that in the earlier practice, when oils were used as collectors a condition of over-oiling was known, similar in general appearance to over-flocculation except that the excess of oil modified qualities of the aggregates of mineral more into a true resemblance of mayonnaise. The only remedy in these cases was to cut down the amounts of oils used andno advantage could be taken of oils which might show strong fiocculating characteristics to be mixed with oils of weaker fiocculating characteristics. In fact, none of them were very strong flocculators and over-flocculation was not observed with minor amounts of these oils. Such success as was had by use of mixtures in the earlier practice was arrived at by empirical methods and to the best of our knowledge the deliberate scientific control of froth quality by simultaneous use of strongly and weakly collecting or fiocculating agents in variable and controllable amounts and proportions has never been known.

While we have described the joint use of amyl and ethyl xanthates in a lime circuit in particular as an example of controlling over-flocculation by a strong collecting reagent, we do not wish to be limited to this particular combination, but we wish to claim as our invention the joint use of several collecting reagents for the exact control of degree of flocculation in order to get the best possible flotation froths and highest yields.

What we claim is:

1. The method of concentrating minerals by flotation which comprises subjecting the mineral in the form of a pulp to a froth flotation operation in the presence of an ethyl xanthate and a higher alcohol xanthate in predetermined proportions.

2. The method of concentrating minerals by flotation which comprises subjecting the mineral in the form of a pulp to a froth flotation operation in the presence of an ethyl xanthate and an amyl xantha'te in predetermined proportions.

3. The method of concentrating minerals by flotation which comprises subjecting the mineral in the form of. a pulp to a froth flotation operation in the presence of sodium ethyl xanthate and potassium amyl xanthate in predetermined proportions.

\ LYLE M. BARKER.

OREL E. YOUNG. OLIVER C. RALSTON. 

